Lesion prediction based in part on tissue characterization

Abstract

A method for determining a predicted lesion size formed in a tissue by receiving or calculating a measure of contact force between the electrode and the tissue, determining a tissue characterization, and calculating the predicted lesion size using both the measure of contact force and the tissue characterization. A system comprising an electronic control unit configured to receive or determine a measure of contact force between the electrode and the tissue, characterize the tissue based on both the measure of impedance and the measure of contact force, and cause the tissue characterization to be either (a) presented to a user, or (b) applied to calculate a metric and cause the metric to be presented to the user.

What is claimed is: 
     
       1. A system, comprising:
 an electronic control unit (ECU) configured to:
 measure an impedance at an interface between an electrode of a catheter and tissue of a patient; 
 measure contact force between the electrode and the tissue; 
 calculate a ratio of the measure of impedance and the measure of contact force, wherein the calculated ratio comprises a fraction which utilizes the measure of impedance as one of the numerator or the denominator and the measure of contact force as the other of the numerator or the denominator; and 
 characterize the tissue for a clinician by presenting the calculated ratio, or by calculating a metric utilizing the calculated ratio and presenting the metric to the clinician. 
 
 
     
     
       2. The system of  claim 1 , wherein the measure of impedance comprises a complex impedance, and (i) a resistance and a reactance of the complex impedance or (ii) a magnitude and a phase angle of the complex impedance is the one of the numerator or the denominator, and the measure of contact force is the other of the numerator or the denominator and the measure of contact force is the other of the numerator or denominator. 
     
     
       3. The system of  claim 1 , wherein the ECU is configured to cause the tissue characterization to be presented to the clinician by adding the tissue characterization to a map or model of the tissue and causing the map or model to be displayed. 
     
     
       4. The system of  claim 1 , wherein the metric is indicative of a surface size and depth of a lesion in the tissue in response to an ablation energy delivered to the tissue during an ablation therapy. 
     
     
       5. The system of  claim 4 , wherein the ECU is further configured to:
 measure energy applied between the electrode and the tissue during the ablation therapy; and 
 the step of calculating the metric further includes the measure of energy applied as an input. 
 
     
     
       6. The system of  claim 5 , wherein the calculated ratio utilizes the measure of impedance as the denominator, and the measure of contact force as the numerator. 
     
     
       7. The system of  claim 1 , further comprising:
 a signal generator configured to be electrically coupled with the electrode and to output a signal to the electrode for assessing the impedance between the electrode and the tissue, wherein the impedance is a complex impedance; and 
 an optical signal source configured to be operatively coupled with a force sensor for providing the measure of contact force between the electrode and the tissue. 
 
     
     
       8. A system, comprising:
 an electronic control unit (ECU) configured to:
 receive or determine a measure of energy applied from an electrode to tissue of a patient; 
 receive or determine a measure of an impedance between the electrode and the tissue; 
 receive or determine a measure of contact force between the electrode and the tissue; 
 calculate a ratio of the measure of impedance to the measure of contact force, where the measure of impedance is the denominator and the measure of contact force is the numerator, wherein the impedance is a complex impedance and the ECU is further configured to calculate the denominator of the ratio based on at least a reactance and a resistance of the complex impedance, or a magnitude and a phase angle of the complex impedance; 
 calculate a size of a lesion in the tissue according to the measure of energy applied and the ratio of the measure of impedance to the measure of contact force; and 
 display lesion size to a clinician. 
 
 
     
     
       9. The system of  claim 8 , wherein receiving or determining the measure of energy applied includes measuring instantaneous power and a duration of energy application, wherein the ECU is further configured to calculate the size of the lesion according to the measure of instantaneous power, the duration of energy application, and the ratio of impedance and force. 
     
     
       10. The system of  claim 8 , wherein the ECU is further configured to cause the lesion size to be presented to a user by adding the lesion depth to a map or model of the tissue and causing the model to be displayed. 
     
     
       11. The system of  claim 10 , wherein the lesion size is indicative of one or more of a depth, a width, and a volume of the lesion. 
     
     
       12. A system comprising:
 a medical catheter including a force sensor and an electrode; and 
 an electronic control unit (ECU) electrically and/or communicatively coupled to the force sensor and the electrode, the ECU configured and arranged to
 measure electrical parameters at an interface between the electrode and target tissue of a patent, 
 measure contact force between the electrode and the target tissue via the force sensor, 
 measure energy applied from the electrode to the target tissue during an ablation therapy; 
 determine lesion size index according to an equation
   LSI( F,I,t )= k   1 ( f   2 (1− e   F/f     1   )+ f   0 )* i   2 (1− e   −(I/i     1     )     2   )*((1− k   0 )+ k   0 1− e   −t/τ /1− e   −T/τ ),
 
 
 
 
       wherein F is force in grams, I is current in milliamps, t is a time in seconds, f 0 , f 1 , and f 2  are force parameter coefficients, i 1  and i 2  are electrical current coefficients, k 0  is a diffusive heating coefficient, k 1  is a rescaling coefficient, τ is a characteristic time value, and the output LSI is in millimeters,
 determine electrical coupling index, 
 based upon at least one of the determined lesion size index, electrical coupling index and measured energy, characterize the tissue, 
 based upon at least one of the determined lesion size index, electrical coupling index and measured energy, predict lesion size and depth of the ablation therapy, and 
 output the tissue characterization and lesion size and depth to a clinician. 
 
     
     
       13. The system of  claim 12 , wherein the electrical parameters comprise a complex impedance. 
     
     
       14. The system of  claim 13 , wherein the electrical coupling index is calculated in accordance with the following equation:
   ECI= a* R +b* X +c    
 
       where  R  and  X  are the mean values of a resistance and reactance of the complex impedance, respectively, and a, b, and c are experimentally-determined coefficients associated with the specific equipment used for measurement.